A federated database system is a database management system (DBMS) that integrates data from multiple autonomous data sources into a single virtual database, referred to as a federated database. The various data sources may be implemented by any suitable resource for storing and retrieving data, including relational database management systems, text files, and/or web services. The federated database system allows data from all the constituent data sources to be accessed using a single database query without physically merging the databases into a single database.